The cytochrome P450s metabolize a wide variety of xenobiotic and endogenous compounds. Biochemical, biophysical, and computational approaches were applied to elucidate the structure-function relationships which govern the interactions of P450s with substrates, inhibitors, membrane lipids, and microsomal proteins. Since these interactions modulate P450 activity, elucidation of their molecular mechanism will aid in (1) clarifying the mechanism of P450-mediated drug and carcinogen metabolism; (2) defining the role of individual P450s in the metabolism of endogenous and environmental chemicals; and (3) development of specific P450 inhibitors.Previous kinetic data on CO binding to P450 were analyzed using the Maximum Entropy Method. This analysis yields kinetic distribution profiles that correspond to P450 conformational landscapes. The results show that P450 1A1 and 3A4 structures are best defined as distributions of conformers. Addition of substrate modified thedistributions. In contrast, a single conformation was observed for P450 2E1.A homology model of human P450 1A2 was generated, and the predicted active site was used to computationally searched a small molecule database for complementary molecules. Several P450 inhibitors were identified by this approach. In addition, mutation of residues in this site modified the catalytic activity. These results thus provide support for our P450 homology model.